A flip-chip package includes a direct electrical connection of a down-facing (that is, “flipped”) semiconductor chip onto a substrate, such as a ceramic substrate or a circuit board, using conductive bumps. Flip-chip technology is quickly replacing older wire bonding technology that uses up-facing chips with conductive wires to connect bond pads on chips to substrates.
Previous processes for flip-chip packaging include multiple steps that could cause problems to a resulting package. One process includes the sequential steps of attaching a die to a substrate, reflowing the connections between the die and substrate, applying a flux clean, dispensing underfill between the substrate and die, curing the underfill, applying a molding, curing the molding, dipping ball grid array (BGA) bond pads in flux, dropping the solder balls on the BGA bond pads, and reflowing the solder balls. These multiple processing steps before the solder ball drop may lead to problems with formed solder balls. For example, the application of heat, moisture, and chemicals in previous steps may result in BGA bond pad contamination and oxidation that cause a missing ball from a BGA bond pad or misalignment of the ball on the BGA bond pad. The application of heat may arise from previous reflowing, baking, and/or curing. Moisture may be caused by a flux clean and/or scan modes of Scanning Acoustic Tomography (C-SAM or T-SAM). Chemicals may come from the flux, flux clean solvent, underfill, and/or molding compound.
The process may cause other problems to the package. For example, delamination of an extra low-k (ELK) dielectric layer in the die may result from the process. Also, underfill delamination may result. Other reliability concerns may arise from the process, such as the formation of cracks in bumps on the die, pre-solder cracking, and chip via burn out.